1. MEIOSIS

2. Diploid Cells 2 sets of chromosomes in a cell. ½ from mom, ½ from dad.
All body cells are diploid
Made by mitosis

3. Haploid Cells 1 set of chromosomes in a cell. 1n
All sex cells are haploid
Made by meiosis

4. Meiosis Notes Gametes: Another name for sex cells: egg & sperm
Zygote: A fertilized cell
2 gametes that are now together

5. Meiosis The making of gametes (eggs & sperm).
Cells contain ½ the normal amount of chromosomes. (haploid)

6. Why is Meiosis Necessary?
To make sex cells or gametes

7. What is Produced by Meiosis?
Four haploid cells (1n)
Each cell is genetically different!

8. Meiosis Quick Review
Makes 4 cells genetically different from parent cell & from each other
Makes 1n cells (1n or 2n?)
Makes gametes
Used for reproduction

9. What is different about meiosis?
Many different variations in the gametes because of crossing over. Crossing over is when tetrads bind tightly, parts break off and are swapped between the chromatids
Divides twice, but only copies DNA once.
Tetrad: when 2 homologous chromosomes bind together during prophase I of meiosis.

10. Meiosis I: Separating the Homologues
Prophase I
Chromosomes appear
Crossing-over occurs between chromosomes (now tetrads)
Nuclear membrane disappears
Metaphase I
Tetrads line up at the equator (middle)

11. Meiosis I: Separating the Homologues
Anaphase I
Tetrads separate and move to opposite ends of the cell
Telophase I/Cytokinesis
Cytoplasm divides & 2 daughter cells are formed
Each cell has a homologous chromosome

12. Meiosis II: Separating the Replicated Chromosomes
Prophase II
Nuclear membrane disappears
Metaphase II
Chromosomes line up along equator (not in homologous pairs)

13. Meiosis II: Separating the Replicated Chromosomes
Anaphase II
Replicated Chromorosomes separate and move to opposite ends of the cell
Telophase II/Cytokinesis
Cytoplasm divides
New membranes are formed
4 HAPLOID daughter cells formed
Each contains ONE chromosome from each homologous pair

16. Mistakes in Meiosis

17. Mistakes in Meiosis
Nondisjunction: when homologous chromosomes fail to separate from each other during meiosis
Result: One gamete may have too many chromosomes, while the other new gamete is missing that chromosome

18. Mistakes in Meiosis
Organisms with extra chromosomes can survive; organisms with too few usually do not survive
Polyploidy: when organisms have more than the normal number of chromosome sets
Can be lethal for animals but not plants (plants just usually get bigger)

19. Examples of Nondisjunction
Turner’s Syndrome
Genotype: Females-X
Absence of one sex chromosome-always female
Diagnosis via amniocentesis
About 30 percent of females with Turner syndrome have extra folds of skin on the neck (webbed neck), a low hairline at the back of the neck, puffiness or swelling (lymphedema) of the hands and feet, skeletal abnormalities, or kidney problems.
Trisomy X
Genotype: Females-XXX
no unusual physical features
or medical problems
Diagnosis usually doesn’t occur
Although females with this condition may be taller than average, this chromosomal change typically causes no unusual physical features. Most females with triple X syndrome have normal sexual development and are able to conceive children.

20. Klinefelter’s Syndrome
Males-XXY-males have an extra X chromosome-1 out of every 1,000 males
MOST COMMON
Affected individuals typically have small testes that do not produce as much testosterone as usual.
Jacob’s Syndrome
Males-XYY-male receives an extra Y chromosome
Hard to determine-no unusual physical features or medical problems
XYY syndrome is associated with an increased risk of learning disabilities and delayed development of speech and language skills. Delayed development of motor skills (such as sitting and walking), weak muscle tone (hypotonia), hand tremors or other involuntary movements (motor tics), and behavioral and emotional difficulties are also possible.

21. Down Syndrome Patau’s Syndrome Trisomy 21-extra 21st chromosome
some impairment of cognitive
ability and physical growth, and a
particular set of facial characteristics
Patau’s Syndrome
Trisomy 13-extra 13th chromosome
Polydactyly—extra digits
associated with severe intellectual disability and physical abnormalities in many parts of the body. Individuals with trisomy 13 often have heart defects, brain or spinal cord abnormalities, very small or poorly developed eyes (microphthalmia), extra fingers or toes, an opening in the lip (a cleft lip) with or without an opening in the roof of the mouth (a cleft palate), and weak muscle tone (hypotonia).

22. Edward’s Syndrome Trisomy 18—extra 18th chromosome
About 95% die before birth
Of liveborn infants, only 50% live to 2 months, and only 5–10% will survive their first year of life
heart abnormalities, kidney malformations, and other internal organ disorders

23. Comparing Mitosis and Meiosis
DNA replicates in interphase
ONE division of chromosomes
Separate sister chromatids
TWO divisions of chromosomes
Separate homologous chromosomes (meiosis I)
Separate sister chromatids (meiosis II)
Makes 2 identical DIPLOID cells
Makes 4 HAPLOID cells
Chromosome # is identical to parent cell
Chromosome # is HALF of the parent cell
Used for replacing old cells, growth
Used to make gametes